How to Hide/Show Searchbar & Toolbar while scrolling the listview in Xamarin forms PCL?

I have a list view, i need to hide toolbar/Navigation bar while scrolling. I have followed this tutorial for Search bar. It is working while appearing disappearing screen is flickering. I need to show/hide like whatsapp. I have attached one sample image. Please help me to achieve this in Xamarin forms PCL. Image may be NSFW.
Clik here to view.